The present invention concerns an injection syringe of the type having a syringe body provided with an injection needle and an actuation pusher mounted so as to be able to move in the body, the syringe having a movable guard for protecting the injection end of the needle, which guard is able to move with respect to the body between a position in which it is retracted in the body away from the injection end of the needle and an active protection position in which the front end of the guard is at the front of the injection end of the needle, the guard and the body having associated projecting and recessed reliefs for holding the guard in a retracted position.
A syringe of this type is described for example in the document FR-A-2.757.066.
In this document, the movable guard of the injection end of the needle has legs entering inside the syringe.
The legs have projections adapted to cooperate with the front wall of the body of the syringe in order to keep the guard in its retracted position. The elasticity of the legs of the guard enable the projections to be left free and thus enable the guard to be released.
In practice, it is found that, if a very violent push is exerted on the actuation pusher during injection, the pressure exerted on the needle guard is such that this may be released and move forwards. The intermediate perforatable piston of the syringe being moved forwards, and it is then no longer possible to inject all the content of the syringe.